(1) Field of the Invention
The rock bolts used in tunneling work to support the natural ground at the inner periphery of the tunnel are classified broadly into the tightening type and the overall adhesion type. The present invention relates to an improvement in the overall adhesion type rock bolt.
(2) Description of the Prior Art
In order to settle a rock bolt in a hole bored in the inner periphery of a tunnel, the rock bolt used in conventional practice is provided with a tubular resilient element or the like securely fitted on one end of the bolt body to fix the bolt body in the interior of the hole and to plug the mouth of the hole. The rock bolt is inserted into the hole and is fixed therein by means of the resilient element or the like, and at the same time the mouth of the hole is plugged by the resilient element or the like. Thereafter packing material such as mortar or cement paste is directly fed into the hole to fill its interior. However, this structure involves a troublesome insertion of the rock bolt into the hole in that the resilient element is fitted on the bolt body. Furthermore, there is a disadvantage of imperfect plugging of the mouth of the hole when the hole has uneven inner wall surfaces adjacent to the mouth. More particularly, while the resilient element which is a manufactured product having a certain outer shape is used to plug the hole, the mouth of the hole may have a larger diameter than expected or may become rugged because it crumbles depending on the nature of the soil or due to vibrations of the boring work. Therefore, the resilient element having a predetermined shape is not always effective to plug the mouth of the hole. Consequently, the packing material injected into the hole will flow out through the gap between the resilient element and the opposed soil.
Besides the tubular resilient element, varied structures have been practised as means for plugging such holes but most of them are complicated or involve many components.